Airlines are currently investigating solutions to provide broadband connectivity for their passengers. Candidates are for instance commercial systems as Long-Term Evolution (LTE), which has been standardized as the successor of the Universal Mobile Telecommunications System (UMTS). For the downlink transmission, i.e. the direction from a Base Station (BS), e.g. NodeB or eNodeB, to a mobile terminal or User Equipment (UE), LTE utilizes Orthogonal Frequency Division Multiple Access (OFDMA) as the physical layer technique which enables high data rate transmission, particularly in frequency selective fading scenarios. LTE as the technology basis for a terrestrial cellular Direct Air-to-Ground (DA2G) communication system is a favorable option for the airlines' continental fleets compared to satellite solutions due to the provision of higher bandwidth at lower cost. Similar considerations may apply for railway companies.
The LTE air interface is optimized for terrestrial cellular networks. In the terrestrial environment there is a lot of fading in mobile communication channels and propagation loss is often much heavier than free space loss due to the presence of buildings and other obstacles. In the direct air-to-ground scenario, wherein a terrestrial mobile communication network is used for communication between a mobile terminal located in an aircraft and a ground-located base station, some partial fading may still occur but it will be typically much less severe than the fading that a terrestrial User Equipment (UE) on the ground may encounter. Instead, the DA2G scenario is characterized by a wireless communication channel with a dominating Line-Of-Sight (LOS) component.
However, depending on the position of an antenna on the body of an airplane and a direction to an associated base station on the ground shadowing due to the body of the plane, its wings, etc. may occur. Therefore conventional systems use multiple antennas at different positions on the airplane in order to overcome potential shadowing.